This invention relates to an integrated optical device and more specifically to rib waveguides and to particular forms of buried layers used in waveguides or other devices.
Rib waveguides (also known as ridge waveguides) are known and are used, in particular, in silicon-on-insulator (SOI) devices. Further details of these are given in WO95/08787 and the references mentioned therein. Essentially, a rib waveguide comprises a slab region with a rib projecting from a major face of the slab region. The optical mode is guided by the rib and part of the slab region from which the rib projects.
With the increasing use of rib waveguides and optical devices integrated on SOI chips, greater flexibility in the form and design of the waveguides and other integrated optical components is required to minimise optical losses and to allow the fabrication of more complex devices.
According to a first aspect of the invention, there is provided a rib waveguide structure comprising a layer of light conductive material defined between two substantially planar faces with a rib formed on one of the faces and an optical component optically coupled to the other face.
According to a second aspect of the invention, there is provided a rib waveguide formed within a substrate, the waveguide comprising a light conductive layer defined between two substantially planar faces with a rib formed on one of the faces, wherein the rib projects from the light conductive layer into the substrate.
According to a third aspect of the invention, there is provided an integrated optical device comprising a light conductive layer separated from a substrate by a layer of light confining material wherein said layer of light confining material is non-planar.
According to a fourth aspect of the invention, there is provided an integrated optical device comprising two or more layers of light confining material buried within a substrate with a light conducting component at least part of which is formed between planes defined by said two layers of light confining material.
According to a fifth aspect of the invention there is provided a method of forming an integrated optical device in which:
a substrate comprising first and second buried layers of light confining material is selected or formed, the first buried layer being closer to an outer surface of the substrate than the second buried layer;
etching trenches in the substrate extending from the first buried layer to the second buried layer;
filling the trenches with material having a refractive index lower than that of the substrate; and
increasing the thickness of the substrate on the side of the first buried layer facing away from the second buried layer.
Preferred and optional features of each aspect of the invention will be apparent from the following description and from the subsidiary claims of the specification.